The invention relates to a circuit arrangement with a pair of switching contacts made from silver and/or a silver alloy and with an inductive load which can be connected to a DC voltage source via the pair of switching contacts.
Inductive loads in DC circuits occur, for example, in automobiles where ever more DC motors are being used owing to the increase in comfort and safety. In particular, in safety systems, for example the anti-skid system, there is a need for a long lifetime in operating cycles, but also for a high switching reliability, that is to say a low failure rate, in the range of use of the switching device, specifically the relay or switch. Both criteria, lifetime and failure rate, are strongly influenced by the material migration of the contacts during switching operation under load in the case of direct current. Of importance in this case is the formation of tips and holes on the contacts which, from the statistical point of view, are highly likely to lead to premature mechanical sticking of the contacts.
The phenomenon of material migration has been known for a long time. It has already been proposed several times to keep this effect as slight as possible by selecting specific alloys and specific pairs of contacts. Such silver alloys are described, for example, in EP 0 448 757 A1. However, in the case of selecting the contact materials purely from the point of view of material migration there is the risk that other contact properties cannot be selected optimally.
Another known possibility of avoiding material migration consists in employing circuit technology to intercept the arc by means of spark-quenching elements. However, such a supplementary circuit is costly.